Conventional GaN-based high electron mobility transistors (HEMTs) are known to have a wide bandgap (3.4 eV) and a high electron saturation velocity (2.5×107cm2/s), and are suitable for high frequency power amplifier applications. FIG. 1 illustrates a conventional HEMT that includes a substrate 10, a buffer layer 11 formed on the substrate 10, a GaN active layer 12 formed on the buffer layer 11, an AlGaN barrier layer 13 formed on the active layer 12, source and drain ohmic contacts 14, 15 formed on the barrier layer 13, a gate electrode 16 of a Schottky contact formed on the barrier layer 13, and a protection layer 17 formed on the source and drain electrodes 14, 15, the gate electrode 16 and the barrier layer 13. Conventionally, the source electrode 14 is spaced apart from the drain electrode 15 by a distance (source-to-drain distance, LSD) that is typically around 2 μm.
Performance of the conventional HEMT at high frequencies must be enhanced for use as a radio frequency (RF) transistor.